Biology subjects

Jordan, M. A.

Publications and source records attributed to Jordan, M. A..

4 recordsLinked to original sources

bioRxiv2026

Structural mechanism of nuclear membrane sealing by LEM2-ESCRT-III

In open mitosis, re-establishing nucleocytoplasmic compartmentalization requires the LEM2-ESCRT machinery to coordinate spindle clearance with sealing of the remaining nuclear envelope pores. The structural basis of this topologically unique and fundamental membrane-remodeling process is poorly understood. Here, we combine biochemical reconstitution, cryo-electron tomography, subtomogram averaging and large-scale molecular dynamics simulations to define the structural mechanism of nuclear membrane sealing. We structurally resolve that LEM2s winged-helix domain (WH) co-polymerizes with the ESCRT-II/III protein CHMP7 to form a membrane-bound scaffold whose geometry is progressively remodeled by downstream ESCRT-III proteins as it transitions from the flat membrane surrounding the pore towards the negatively curved membrane neck. In parallel, LEM2 positions its intrinsically disordered low-complexity domain within the pore, where condensation around spindle microtubules mechanically couples the membrane-ESCRT-LEM2 scaffold to the spindle and narrows the remaining diffusion path, restoring compartmentalization before membrane closure is complete. Remarkably, the LEM2-WH domain alone forms tightly constricted membrane tubes, coating the negatively curved inner surface, revealing an intrinsic membrane-remodeling activity of the receptor itself. Together, our work establishes a structural framework for how receptor-ESCRT co-polymerization, low complexity domain-mediated sealing and receptor-driven membrane remodeling guide nuclear-envelope pores from spindle-containing openings to terminal constriction and fusion.

molecular biology↗

bioRxiv2025

A protein-DNA surface hydrogel mechanically protects the cell nucleus

The nuclear envelope protects the genome from mechanical stress during processes such as migration, division, and compression1-6, but how it buffers forces at the scale of DNA remains unclear. Here, we utilize optical tweezers to show that a multivalent protein-DNA co-condensate containing the nuclear envelope protein LEM27,8 and the DNA-binding protein BAF 9,10 shield DNA beyond its melting point at 65 pN11. Under load, their collective assembly induces an unconventional DNA stiffening effect that provides mechanical reinforcement, dependent on the intrinsically disordered region (IDR) of LEM2. At the nuclear surface, these components form an elastic surface hydrogel in which LEM2 IDR-IDR interactions contract the surface hydrogel relative to its relaxed state, introducing a pre-stress in the lamin network. Inside cells, this surface hydrogel model can recapitulate elastic properties of the nuclear envelope measured via AFM indentation experiments as well as nuclear morphology, using parameters obtained at the molecular scale by use of optical tweezers. Disruption of the surface hydrogel increases DNA damage and micronuclei formation during nuclear deformation. These findings reveal a load-bearing, mesoscale surface hydrogel that reinforces the nucleus and expands the functional repertoire of biomolecular condensates to include DNA protection under mechanical stress.

biophysics↗

bioRxiv2022

Integrative modeling reveals the molecular architecture of the Intraflagellar Transport A (IFT-A) complex

Intraflagellar transport (IFT) is a conserved process of cargo transport in cilia that is essential for development and homeostasis in organisms ranging from algae to vertebrates. In humans, variants in genes encoding subunits of the cargo-adapting IFT-A and IFT-B protein complexes are a common cause of genetic diseases known as ciliopathies. While recent progress has been made in determining the atomic structure of IFT-B, little is known of the structural biology of IFT-A. Here, we combined chemical cross-linking mass spectrometry and cryo-electron tomography with AlphaFold2-based prediction of both protein structures and interaction interfaces to model the overall architecture of the monomeric six-subunit IFT-A complex, as well as its polymeric assembly within cilia. We define monomer-monomer contacts and membrane-associated regions available for association with transported cargo, and we also use this model to provide insights into the pleiotropic nature of human ciliopathy-associated genetic variants in genes encoding IFT-A subunits. Our work demonstrates the power of integration of experimental and computational strategies both for multi-protein structure determination and for understanding the etiology of human genetic disease. SummaryThe 3D structure of the six-subunit complex and its polymeric assembly gives insights into cargo transport in cilia and how specific mutations in these genes lead to ciliopathy birth defects.

biochemistry↗

bioRxiv2021

In situ architecture of the ciliary base reveals the stepwise assembly of IFT trains

The cilium is an antenna-like organelle that performs numerous cellular functions, including motility, sensing, and signaling. The base of the cilium contains a selective barrier that regulates the entry of large intraflagellar transport (IFT) trains, which carry cargo proteins required for ciliary assembly and maintenance. However, the native architecture of the ciliary base and the process of IFT train assembly remain unresolved. Here, we use in situ cryo-electron tomography to reveal native structures of the transition zone region and assembling IFT trains at the ciliary base. We combine this direct cellular visualization with ultrastructure expansion microscopy to describe the front-to-back stepwise assembly of IFT trains: IFT-B forms the backbone, onto which IFT-A, then dynein-1b, and finally kinesin-2 sequentially bind before entry into the cilium. One Sentence SummaryNative molecular structure of the ciliary transition zone and hierarchical order of IFT assembly visualized within Chlamydomonas cells.

cell biology↗